Too Hot to Handle: A Case of Fever of Unknown Origin.

Fever of unknown origin (FUO) is defined as a fever higher than 38.3ºC for at least three weeks. It remains a difficult diagnostic challenge and it carries well over 200 differential diagnoses, including infectious, rheumatologic and malignant etiologies. A methodological approach with clinical deductive reasoning and value-based investigative work-up can establish the diagnosis. This case is about a 76-year-old male with a past medical history of atrial fibrillation, bladder cancer treated with chemotherapy (now in remission) and hydronephrosis with recent ureteropelvic junction stent placement. He presented to the emergency department (ED) for worsening shortness of breath (SOB), weakness, and fevers. His initial workup was notable for a urinary tract infection which was treated with ceftriaxone. However, there was only a limited improvement in the fever. Diagnostic imaging was negative on initial review. He was evaluated by consultants of different specialities including infectious disease, rheumatology, and hematology. Ultimately, the decision was made to discharge the patient home on steroids with further outpatient workup. He returned four weeks later with worsening fever and was found to have new-onset mediastinal lymphadenopathy. A biopsy of an inguinal lymph node was obtained which showed high grade-B cell lymphoma. The patient was continued on prednisone and started on chemotherapeutic agents which included vincristine, rituximab and cyclophosphamide. Shortly after starting treatment, the patient and family elected for hospice. This case demonstrates the importance of continuously questioning the diagnosis at hand and of keeping an open mind when evaluating a patient with FUO.

The melanoma-linked "redhead" MC1R influences dopaminergic neuron survival.

OBJECTIVE: Individuals with Parkinson disease are more likely to develop melanoma, and melanoma patients are reciprocally at higher risk of developing Parkinson disease. Melanoma is strongly tied to red hair/fair skin, a phenotype of loss-of-function polymorphisms in the MC1R (melanocortin 1 receptor) gene. Loss-of-function variants of MC1R have also been linked to increased risk of Parkinson disease. The present study is to investigate the role of MC1R in dopaminergic neurons in vivo. METHODS: Genetic and pharmacological approaches were employed to manipulate MC1R, and nigrostriatal dopaminergic integrity was determined by comprehensive behavioral, neurochemical, and neuropathological measures. RESULTS: MC1Re/e mice, which carry an inactivating mutation of MC1R and mimic the human redhead phenotype, have compromised nigrostriatal dopaminergic neuronal integrity, and they are more susceptible to dopaminergic neuron toxins 6-hydroxydopamine and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Furthermore, a selective MC1R agonist protects against MPTP-induced dopaminergic neurotoxicity. INTERPRETATION: Our findings reveal a protective role of MC1R in the nigrostriatal dopaminergic system, and they provide a rationale for MC1R as a potential therapeutic target for Parkinson disease. Together with its established role in melanoma, MC1R may represent a common pathogenic pathway for melanoma and Parkinson disease. Ann Neurol 2017;81:395-406.

Systematic Review and Meta-Analysis on the Influence of Surgeon Specialization on Outcomes Following Appendicectomy in Children.

The aim of this study is to assess the influence of surgeon specialization on outcomes following appendicectomy in children.General surgeons and pediatric surgeons manage appendicitis in children; however, the influence of subspecialization on outcomes remains unclear.Two authors searched Medline and Embase to identify relevant studies. Eligible studies were comparative and provided data on children who had appendicectomy while under the care of general or pediatric surgical teams. Two authors initially screened titles and abstracts and then full text manuscripts were evaluated. Data were extracted by 2 authors using an electronic spreadsheet. Pooled risk ratios and pooled mean differences were used in analyses.We identified 9 relevant studies involving 50,963 children who were managed by general surgery teams and 15,032 children who were managed by pediatric surgery teams. A normal appendix was removed in 4660/48,105 children treated by general surgery units and in 889/14,760 children treated by pediatric units (pooled risk ratio 1.79; 95% confidence interval [CI] 1.26-2.54; P = 0.001). Children managed in general units had shorter mean hospital stays compared with children managed in pediatric units (pooled mean difference -0.70 days; 95%CI -1.09 to -0.30; P = 0.0005). There were no significant differences regarding wound infections, intra-abdominal abscesses, readmissions, or mortality.We found that children who were managed by specialized pediatric surgery teams had lower rates of negative appendicectomy although mean length of stay was longer. Our article is based upon a group of heterogeneous and mostly retrospective studies and therefore there is little external validity. Further studies are needed.

Cardiotoxicity and cardioprotection in childhood cancer.

Children diagnosed with cancer are now living longer as a result of advances in treatment. However, some commonly used anticancer drugs, although effective in curing cancer, can also cause adverse late effects. The cardiotoxic effects of anthracycline chemotherapy, such as doxorubicin, and radiation can cause persistent and progressive cardiovascular damage, emphasizing a need for effective prevention and treatment to reduce or avoid cardiotoxicity. Examples of risk factors for cardiotoxicity in children include higher anthracycline cumulative dose, higher dose of radiation, younger age at diagnosis, female sex, trisomy 21 and black race. However, not all who are exposed to toxic treatments experience cardiotoxicity, suggesting the possibility of a genetic predisposition. Cardioprotective strategies under investigation include the use of dexrazoxane, which provides short- and long-term cardioprotection in children treated with doxorubicin without interfering with oncological efficacy, the use of less toxic anthracycline derivatives and nutritional supplements. Evidence-based monitoring and screening are needed to identify early signs of cardiotoxicity that have been validated as surrogates of subsequent clinically significant cardiovascular disease before the occurrence of cardiac damage, in patients who may be at higher risk.

Anatomy and bronchoscopy of the porcine lung. A model for translational respiratory medicine.

The porcine model has contributed significantly to biomedical research over many decades. The similar size and anatomy of pig and human organs make this model particularly beneficial for translational research in areas such as medical device development, therapeutics and xenotransplantation. In recent years, a major limitation with the porcine model was overcome with the successful generation of gene-targeted pigs and the publication of the pig genome. As a result, the role of this model is likely to become even more important. For the respiratory medicine field, the similarities between pig and human lungs give the porcine model particular potential for advancing translational medicine. An increasing number of lung conditions are being studied and modeled in the pig. Genetically modified porcine models of cystic fibrosis have been generated that, unlike mouse models, develop lung disease similar to human cystic fibrosis. However, the scientific literature relating specifically to porcine lung anatomy and airway histology is limited and is largely restricted to veterinary literature and textbooks. Furthermore, methods for in vivo lung procedures in the pig are rarely described. The aims of this review are to collate the disparate literature on porcine lung anatomy, histology, and microbiology; to provide a comparison with the human lung; and to describe appropriate bronchoscopy procedures for the pig lungs to aid clinical researchers working in the area of translational respiratory medicine using the porcine model.

DbVar and DGVa: public archives for genomic structural variation.

Much has changed in the last two years at DGVa (http://www.ebi.ac.uk/dgva) and dbVar (http://www.ncbi.nlm.nih.gov/dbvar). We are now processing direct submissions rather than only curating data from the literature and our joint study catalog includes data from over 100 studies in 11 organisms. Studies from human dominate with data from control and case populations, tumor samples as well as three large curated studies derived from multiple sources. During the processing of these data, we have made improvements to our data model, submission process and data representation. Additionally, we have made significant improvements in providing access to these data via web and FTP interfaces.

Microbial diversity and anaerobic hydrocarbon degradation potential in an oil-contaminated mangrove sediment.

BACKGROUND: Mangrove forests are coastal wetlands that provide vital ecosystem services and serve as barriers against natural disasters like tsunamis, hurricanes and tropical storms. Mangroves harbour a large diversity of organisms, including microorganisms with important roles in nutrient cycling and availability. Due to tidal influence, mangroves are sites where crude oil from spills farther away can accumulate. The relationship between mangrove bacterial diversity and oil degradation in mangrove sediments remains poorly understood. RESULTS: Mangrove sediment was sampled from 0-5, 15-20 and 35-40 cm depth intervals from the Suruí River mangrove (Rio de Janeiro, Brazil), which has a history of oil contamination. DGGE fingerprinting for bamA, dsr and 16S rRNA encoding fragment genes, and qPCR analysis using dsr and 16S rRNA gene fragment revealed differences with sediment depth. CONCLUSIONS: Analysis of bacterial 16S rRNA gene diversity revealed changes with depth. DGGE for bamA and dsr genes shows that the anaerobic hydrocarbon-degrading community profile also changed between 5 and 15 cm depth, and is similar in the two deeper sediments, indicating that below 15 cm the anaerobic hydrocarbon-degrading community appears to be well established and homogeneous in this mangrove sediment. qPCR analysis revealed differences with sediment depth, with general bacterial abundance in the top layer (0-5 cm) being greater than in both deeper sediment layers (15-20 and 35-40 cm), which were similar to each other.

Biomechanical evaluation of four different transosseous-equivalent/suture bridge rotator cuff repairs.

PURPOSE: Evaluate the biomechanical behavior of four variants of the transosseous-equivalent/suture bridge (TOE/SB) repair. METHODS: Four suture bridge (SB) constructs were created using 24 sheep infraspinatus tendon-humerus constructs (n = 6 per technique). The groups were (1) Knotted Standard Suture Bridge (Standard SB)--suture bridge with two medial mattress stitches, (2) Knotted Double Suture Bridge (Double SB)--four medial mattress stitches, (3) Untied Suture Bridge with Medial FT Anchors (Untied SB with FT)--two medial mattress stitches without knots, and (4) Untied Suture Bridge with PushLocks (Untied SB with Pushlocks)--two medial mattress stitches without knots. The contact area footprint was measured with an electronic pressure film prior to dynamic mechanical testing for gapping and testing to failure. RESULTS: The Double SB produced the greatest contact area footprint compared to the other techniques, which did not differ. The Double SB repair with a mean failure load of 456.9N was significantly stronger than the Untied SB with Pushlocks repair at 300N (P = 0.023), the standard SB repair at 295N (P = 0.019), and lastly the Untied SB with FT repair at 284N (P = 0.011). No differences were detected between the two mattress stitch standard SB repair with knots and the knotless two mattress stitch repairs (Untied SB with FT and Untied SB with Pushlocks). Gaps developed during cyclic loading in all repairs apart from the Double SB repair. CONCLUSIONS: The transosseous-equivalent/suture bridge repair with 4 stitches tied in the medial row and maximal lateral suture strand utilization (Double SB) outperformed all other repairs in terms of failure load, tendon-bone contact, and gapping characteristics. The presence of knots in the medial row did not change tendon fixation with respect to failure load, contact area or gapping characteristics.

The MgtC virulence factor of Salmonella enterica serovar Typhimurium activates Na(+),K(+)-ATPase.

The mgtC gene of Salmonella enterica serovar Typhimurium encodes a membrane protein of unknown function that is important for full virulence in the mouse. Since mgtC is part of an operon with mgtB which encodes a Mg(2+)-transporting P-type ATPase, MgtC was hypothesized to function in ion transport, possibly in Mg(2+) transport. Consequently, MgtC was expressed in Xenopus laevis oocytes, and its effect on ion transport was evaluated using ion selective electrodes. Oocytes expressing MgtC did not exhibit altered currents or membrane potentials in response to changes in extracellular H(+), Mg(2+), or Ca(2+), thus ruling out a previously postulated function as a Mg(2+)/H(+) antiporter. However, addition of extracellular K(+) markedly hyperpolarized membrane potential instead of the expected depolarization. Addition of ouabain to block the oocyte Na(+),K(+)-ATPase completely prevented hyperpolarization and restored the normal K(+)-induced depolarization response. These results suggested that the Na(+),K(+)-ATPase was constitutively activated in the presence of MgtC resulting in a membrane potential largely dependent on Na(+),K(+)-ATPase. Consistent with the involvement of Na(+),K(+)-ATPase, oocytes expressing MgtC exhibited an increased rate of (86)Rb(+) uptake and had increased intracellular free [K(+)] and decreased free [Na(+)] and ATP. The free concentrations of Mg(2+) and Ca(2+) and cytosolic pH were unchanged, although the total intracellular Ca(2+) content was slightly elevated. These results suggest that the serovar Typhimurium MgtC protein may be involved in regulating membrane potential but does not directly transport Mg(2+) or another ion.

A study exploring the role of intercostal nerve damage in chronic pain after thoracic surgery.

OBJECTIVE: Our aim was to investigate the prevalence of intra-operative nerve damage and its association with chronic pain. METHODS: Our prospective study of 33 patients used nerve conduction studies to assess intercostal nerve function during elective thoracic surgical procedures. We used two methods to study nerve conduction: pre-operative magnetic stimulation (in 10 patients) and intra-operative nerve conduction studies (in all patients) We correlated these findings with specific intra-operative parameters, pain and psychological questionnaires pre-op and 3 month post-op and altered cutaneous sensation. RESULTS: Magstim (magnetic stimulation) assessments were not reliable and were therefore abandoned. Intraoperative intercostal nerve studies revealed two distinct patterns of nerve injury and also that nerve injury was less in those cases where a rib was not resected. However, intercostal nerve damage detected at the time of operation is not associated with chronic pain or altered cutaneous sensation at 3 months post-op. CONCLUSIONS: The study findings suggest that either the amount of intra-operative intercostal nerve damage is not indicative of long-term nerve damage or that there is a more significant cause for chronic pain other than intercostal nerve injury.

Magnesium transporters: properties, regulation and structure.

The chemistry of Mg2+ is unique amongst biological cations, and the properties of Mg2+ transport systems reflect this chemistry. Prokaryotes carry three classes of Mg2+ transport systems: CorA, MgtA/B and MgtE. CorA and MgtE are widely distributed in both Eubacteria and Archaea, while the MgtA/B class is found primarily in the Eubacteria. Eukaryotic homologs of CorA, although clearly functional as Mg2+ transporters, have minimal sequence homology and include the Mrs2p mitochondrial Mg2+ channel and the ALR proteins of fungi. MgtE homologs are more recognizable in eukaryotes as the SLC41 class of transporters. The MgtA/B Mg2+ transporters belong to the P-type ATPase superfamily, but mediate Mg2+ influx down its electrochemical gradient rather than against the gradient as with other P-type ATPases. Their physiological role is not clear. CorA is the only Mg2+ transporter whose structure has been solved. It is a homopentamer with two transmembrane domains per monomer, the first of which forms the ion conduction pathway. Mg2+ transport involves first the binding of the fully hydrated cation to an extracellular binding loop connecting the transmembrane domains. Passage through the membrane involves no electrostatic interactions, but two cytosolic domains, one carrying extremely high concentrations of positive charge and the other negative charge appear to help control Mg2+ flux, in concert with an intracellular Mg2+ bound between domains of each monomer. Neither CorA nor MgtE appear to be transcriptionally regulated, implying they are primarily "housekeeping" genes. Nonetheless, mutation of the corA gene in Salmonella enterica serovar Typhimurium leads to attenuation of virulence and other defects, even though the strain carries two additional Mg2+ transporters and the mutant exhibits no Mg2+-dependent growth deficit.

A questionnaire study investigating the prevalence of the neuropathic component of chronic pain after thoracic surgery.

OBJECTIVE: Our questionnaire study set out to assess the prevalence of chronic pain after thoracic surgery, the contribution of the neuropathic component of chronic pain and the impact of chronic pain on patients' lives. METHODS: A questionnaire was sent to 1152 patients who had undergone thoracic surgery in our department between 7 months and 7 years ago. The questionnaire was designed specifically for the study and included questions on neuropathic symptoms. Responses were correlated with data from our prospectively entered database for analysis. RESULTS: Nine hundred and forty-eight people were included in the study, of which 600 responded (63%). Prevalence of chronic pain is 57% at 7-12 months, 36% at 4-5 years and 21% at 6-7 years. Patient age, consultant and time since the operation all have significant effects. Surgical approach (video-assisted thoracoscopic surgery, thoracotomy) and diagnosis are not significant. Thirty-nine percent of those with pain take analgesia, 46% felt their pain is their worst medical problem and 40% reported it limits their daily activities. The prevalence of each neuropathic symptom is between 35 and 83%. The presence of a neuropathic symptom is associated with significantly more severe pain, more analgesia use and pain more likely to limit daily activity. CONCLUSIONS: Chronic pain has a significant prevalence and impact on patients' lives for several years after thoracic surgery. Nerve dysfunction is associated with more severe pain, a greater impact and tends to persist. The reason for the individual consultant being an important factor in post-thoracotomy pain needs further investigation.

The Nramp orthologue of Cryptococcus neoformans is a pH-dependent transporter of manganese, iron, cobalt and nickel.

Cryptococcus neoformans is an important human opportunistic pathogen and a facultative intracellular parasite, particularly in HIV-infected individuals. Little is known about metal ion transport in this organism. C. neoformans encodes a single member of the Nramp (natural resistance-associated macrophage protein) family of bivalent cation transporters, known as Cramp, which we have cloned and expressed in Xenopus laevis oocytes and Spodoptera frugiperda Sf 21 insect cells. Cramp induces saturable transport of a broad range of bivalent transition series cations, including Mn2+, Fe2+, Co2+ and Ni2+. Maximal cation transport occurs at pH 5.5-6.0, consistent with the proton gradient-based energetics of other Nramp orthologues. Mn2+ transport is diminished in the presence of 140 mM Na+, compatible with a Na+ slippage mechanism proposed for the Saccharomyces cerevisiae Nramp orthologue Smf1p. Cramp resembles Smf1p with respect to predicted membrane topology, substrate specificity and pH dependence, but differs in terms of its apparent affinity for Mn2+ and negligible inhibition by Zn2+. Cramp is the first Nramp orthologue from a fungal pathogen to be functionally characterized. Insights afforded by these findings will allow the formulation of new hypotheses regarding the role of metal ions in the pathophysiology of cryptococcosis.

The Salmonella enterica serovar typhimurium divalent cation transport systems MntH and SitABCD are essential for virulence in an Nramp1G169 murine typhoid model.

Nramp1 is a transporter that pumps divalent cations from the vacuoles of phagocytic cells and is associated with the innate resistance of mice to diverse intracellular pathogens. We demonstrate that sitA and mntH, genes encoding high-affinity metal ion uptake systems in Salmonella enterica serovar Typhimurium, are upregulated when Salmonella is internalized by Nramp1-expressing macrophages and play an essential role in systemic infection of congenic Nramp1-expressing mice.

The CorA Mg2+ transporter is a homotetramer.

CorA is a primary Mg2+ transporter for Bacteria and Archaea. The C-terminal domain of approximately 80 amino acids forms three transmembrane (TM) segments, which suggests that CorA is a homo-oligomer. A Cys residue was added to the cytoplasmic C terminus (C317) of Salmonella enterica serovar Typhimurium CorA with or without mutation of the single periplasmic Cys191 to Ser; each mutant retained function. Oxidation of the Cys191Ser Cys317 CorA gave a dimer. Oxidation of Cys317 CorA showed a dimer plus an additional band, apparently cross-linked via both Cys317 and C191. To determine oligomer order, intact cells or purified membranes were treated with formaldehyde or carbon disulfide. Higher-molecular-mass bands formed, consistent with the presence of a tetramer. Cross-linking of the Bacillus subtilis CorA expressed in Salmonella serovar Typhimurium similarly indicated a tetramer. CorA periplasmic soluble domains from both Salmonella serovar Typhimurium and the archaeon Methanococcus jannaschii were purified and shown to retain structure. Formaldehyde treatment showed formation of a tetramer. Finally, previous mutagenesis of the CorA membrane domain identified six intramembrane residues forming an apparent pore that interacts with Mg2+ during transport. Each was mutated to Cys. In mutants carrying a single intramembrane Cys residue, spontaneous disulfide bond formation that was enhanced by oxidation with Cu(II)-1,10-phenanthroline was observed between monomers, indicating that these Mg2+-interacting residues within the membrane are very close to their cognate residue on another monomer. Thus, CorA appears to be a homotetramer with a TM segment of one monomer physically close to the same TM segment of another monomer.

Catastrophic haemoptysis during rigid bronchoscopy: a discussion of treatment options to salvage patients during catastrophic haemoptysis at rigid bronchoscopy.

OBJECTIVE: We report a negative experience of fatal haemorrhage during rigid bronchoscopy when an intrabronchial lesion was biopsied. Despite being prepared for and carrying out emergency sternotomy and clamping the lung hilum, the patient died. METHODS: We reviewed mainly non-surgical literature for recommendations for the management of catastrophic bleeding at bronchoscopy. RESULTS: The literature does provide advice for management of 'massive haemoptysis' defined as more than 600 ml in 24 h and 'exsanguinating haemoptysis' which is at least 1000 ml blood loss at a rate more than 150 ml/h. However there is little in the current surgical literature on the immediate treatment of 'catastrophic haemoptysis' which we define as major bleeding from the airway causing an immediate threat to life requiring immediate surgery. Gathering treatment options from various authors we present a suggested protocol for the management of this thoracic surgical emergency. CONCLUSIONS: We recommend the initial salvage treatment to be: (1) wedge the rigid bronchoscope into the haemorrhaging bronchus, (2) tamponade the bleeding site with a balloon-tipped vascular catheter, (3) remove the bronchoscope and intubate with a double-lumen tube, (4) undertake emergency definitive surgery. We strongly recommend that a suitable catheter be kept immediately available for this very rare but dangerous complication.

Lung volume reduction surgery in a ventilator-dependent patient.

In recent years lung volume reduction surgery (LVRS) has been advocated in a selected group of severe chronic obstructive pulmonary disease (COPD) patients. There are few reports of successful surgical intervention on ventilator-dependent patients. We present our own experience with a 53-year-old male who suffered an acute exacerbation of COPD and who could not be weaned off ventilation after 22 days. He underwent bilateral LVRS after which he was successfully weaned from ventilation. He is alive 4 years later with a satisfactory quality of life.

Is an early invasive approach superior to a conservative strategy in patients with acute coronary syndrome?

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether an early invasive approach (involving early coronary angiography followed by revascularisation if suitable) is superior to a conservative approach (with revascularisation only in patients with failed medical therapy) in patients with acute coronary syndrome. Altogether 282 papers were found using the reported search, of which seven presented the best evidence to answer the clinical question. The author, journal, date and country of publication, patient group studied, study type, relevant outcomes, results, and study weaknesses of these papers are tabulated. We conclude that in patients diagnosed with acute coronary syndrome, an early invasive approach is clearly superior to a conservative approach.

Changes in human immunodeficiency virus type 1 Gag at positions L449 and P453 are linked to I50V protease mutants in vivo and cause reduction of sensitivity to amprenavir and improved viral fitness in vitro.

Human immunodeficiency virus type 1 (HIV-1) Gag protease cleavage sites (CS) undergo sequence changes during the development of resistance to several protease inhibitors (PIs). We have analyzed the association of sequence variation at the p7/p1 and p1/p6 CS in conjunction with amprenavir (APV)-specific protease mutations following PI combination therapy with APV. Querying a central resistance data repository resulted in the detection of significant associations (P < 0.001) between the presence of APV protease signature mutations and Gag L449F (p1/p6 LP1'F) and P453L (p1/p6 PP5'L) CS changes. In population-based sequence analyses the I50V mutant was invariably linked to either L449F or P453L. Clonal analysis revealed that both CS mutations were never present in the same genome. Sequential plasma samples from one patient revealed a transition from I50V M46L P453L viruses at early time points to I50V M46I L449F viruses in later samples. Various combinations of the protease and Gag mutations were introduced into the HXB2 laboratory strain of HIV-1. In both single- and multiple-cycle assay systems and in the context of I50V, the L449F and P453L changes consistently increased the 50% inhibitory concentration of APV, while the CS changes alone had no measurable effect on inhibitor sensitivity. The decreased in vitro fitness of the I50V mutant was only partially improved by addition of either CS change (I50V M46I L449F mutant replicative capacity approximately 16% of that of wild-type virus). Western blot analysis of Pr55 Gag precursor cleavage products from infected-cell cultures indicated accumulation of uncleaved Gag p1-p6 in all I50V viruses without coexisting CS changes. Purified I50V protease catalyzed cleavage of decapeptides incorporating the L449F or P453L change 10-fold and 22-fold more efficiently than cleavage of the wild-type substrate, respectively. HIV-1 protease CS changes are selected during PI therapy and can have effects on both viral fitness and phenotypic resistance to PIs.

Magnesium transport in Salmonella typhimurium: regulation of mgtA and mgtCB during invasion of epithelial and macrophage cells.

Salmonella typhimurium contains two inducible Mg2+ transport systems, MgtA and MgtB, the latter encoded by a two-gene operon, mgtCB. Mg2+ deprivation of S. typhimurium increases transcription of both mgtA and mgtCB over a thousandfold and a similar increase occurs upon S. typhimurium invasion of epithelial cells. These increases are mediated by the phoPQ two-component signal transduction system, an essential system for S. typhimurium virulence. It was therefore hypothesized that expression of MgtA and MgtCB is increased upon invasion of eukaryotic cells because of a lack of intravacuolar Mg2+. However, when S. typhimurium was grown at pH 5.2, the capacity of the constitutive CorA transporter in mediating Mg2+ was greater than that at pH 7.4. Furthermore, induction of mgtA and mgtCB transcription was greater in the presence of a wild-type corA allele than in its absence. This implies that intravacuolar S. typhimurium could obtain sufficient Mg2+ via the CorA system. The effect of acid pH on mgtA and mgtCB transcription was also measured. Compared to induction at pH 7.4, exposure to pH 5.2 almost completely abolished induction of mgtA at low Mg2+ concentrations but diminished induction of mgtCB only twofold. Adaptation of cells to acid pH by overnight growth resulted in normal levels of induction of mgtA and mgtCB at low Mg2+ concentrations. These results imply an additional level of regulation for mgtA that is not present for mgtCB. Conversely, repression of mgtA and mgtCB expression by increased extracellular Mg2+ was relatively insensitive to acid. Transcription of both loci was strongly induced upon invasion of the Hep-2 or CMT-93 epithelial-like or J774 macrophage-like cell lines. However, the presence or absence of functional alleles of either or both mgtA or mgtCB had no effect on invasion efficiency or short-term survival of S. typhimurium within the eukaryotic cells. It was concluded that the strong Mg(2+)-dependent induction of mgtA and mgtCB upon invasion of eukaryotic cells is not required because S. typhimurium lacks sufficient Mg2+ during eukaryotic cell invasion and initial intravacuolar growth.